Abstract: Foundation scour is a common problem of offshore wind turbine pile foundation and can seriously affect the safety of wind turbine foundation structures. It is, therefore, necessary to conduct in-depth research on the protective measures for offshore wind turbine pile foundation. By using numerical simulation methods, the protective performance of scour protection ring at single pile foundation under the condition of unidirectional flow is studied. A numerical model of water flow-pile foundation-seabed interaction is established by FLOW-3D software. The influences of two parameters, the diameter and the installation height of the protection ring, on the foundation scour are analyzed, and a formula for predicting the scour depth under the case of protection ring installed is given based on the numerical simulation results of the model. It is found that for the protection rings with the same diameter the closer the protection ring is to the seabed, the higher the protection efficiency. When the installation height of the protection rings is 0.04 m, the scour depth decreases by 50%. If the installation height of the rings is 0 m the protection efficiency can achieve the highest. When the protection rings are installed too far away from the seabed, however, they will basically lose their protective function. For the protection rings which are installed closely to the seabed surface, the larger the diameter of the rings, the better the protection efficiency. When the ring diameter is 0.30 m and/or 0.35 m, the scour depth can be reduced by more than 50%. If the ring diameter exceeds a certain limit, however, the time to reach the scour equilibrium will be increased correspondingly with the increase in the diameter of the protection ring. But, the protective effect of the rings is hardly changed.